Modules/constraints: init constraints checking for inventory compatible modules

lib/description.nix

@@ -1,5 +1,63 @@
 { clan-core, lib }:
-rec {
+let
+  getRoles =
+    modulePath:
+    let
+      rolesDir = modulePath + "/roles";
+    in
+    if builtins.pathExists rolesDir then
+      lib.pipe rolesDir [
+        builtins.readDir
+        (lib.filterAttrs (_n: v: v == "regular"))
+        lib.attrNames
+        (lib.filter (fileName: lib.hasSuffix ".nix" fileName))
+        (map (fileName: lib.removeSuffix ".nix" fileName))
+      ]
+    else
+      [ ];
+
+  getConstraints =
+    modulename:
+    let
+      eval = lib.evalModules {
+        specialArgs = {
+          allRoles = getRoles clan-core.clanModules.${modulename};
+        };
+        modules = [
+          ./constraints/interface.nix
+          (getFrontmatter modulename).constraints
+        ];
+      };
+    in
+    eval.config.roles;
+
+  checkConstraints =
+    { moduleName, resolvedRoles }:
+    let
+      eval = lib.evalModules {
+        specialArgs = {
+          inherit moduleName;
+          allRoles = getRoles clan-core.clanModules.${moduleName};
+          resolvedRoles = {
+            controller = {
+              machines = [ "test-inventory-machine" ];
+            };
+            moon = {
+              machines = [ ];
+            };
+            peer = {
+              machines = [ ];
+            };
+          };
+        };
+        modules = [
+          ./constraints/default.nix
+          ((getFrontmatter moduleName).constraints or { })
+        ];
+      };
+    in
+    eval.config.assertions;
+
   getReadme =
     modulename:
     let
@@ -38,4 +96,13 @@ rec {
         ---
         ...rest of your README.md...
       '';
+in
+{
+  inherit
+    getFrontmatter
+    getReadme
+    getRoles
+    getConstraints
+    checkConstraints
+    ;
 }